How does the game know where to save units from histfigs that started without a civilization?

[Shim-Panze]

The game saves units in "unit chunks", which are binary files saved separated from the rest of the world data. When the game needs to load the unit for a historical figure, it grabs its nemesis_record and checks save_file_id for knowing which chunk and member_idx for knowing where in the chunk to load the unit from. But that's for loading, I want to know about saving a new nemesis:
When the game generates a new historical figure (e.g. your adventurer talks to someone), it'll check which civilization the unit belongs to (unit.civ_id), and draw values from the corresponding historical_entity's save_file_id and next_member_idx fields when creating the new nemesis record. When this entity's next_member_idx hits 100, the game then sets it back to 0 and changes save_file_id to the value at df.global.next_unit_chunk_id (and raises this value by 1), thus starting a new unit chunk (each holds 100 units).

However, there are historical figures that don't have any civilization (titans, semi/mega/forgotten beasts, night trolls, animals and animal people generated from the wilds), and by my observations it's very clear that the game draws their nemesis records' save_file_id and member_idx from somewhere in the same manner that it does for civilized beings: some data structure has fields analogous to save_file_id and next_member_idx present in historical_entity. You can talk to a wild animal or animal person in adventure mode to verify this process happening.

I want to know where these fields are located. I looked and experimented a ton with generating civless worlds with tons of beasts, and I also looked through the structure docs for anything that might have "save_file_id", "next_member_idx" and some similar variations, but couldn't find anything.

I have no idea how to even start reverse engineering the game's memory, so I'm asking here in case someone happens to know about this or might want to look into it in the future. Knowing this might give some insight on how the game deals with civless figures in matters that it's already known when it comes to figures with civilizations. Names, for example: I know where to find the language_word_table that the game uses to name figures born into civilizations, but not those without a civ (wild animals, figures made via [LOCAL_POPS_PRODUCE_HEROES], etc.)

[Shim-Panze]

I got my answer from somewhere else.
It's in df.global.world.worldgen, the fields next_unit_chunk_id and next_unit_chunk_offset.
In hindsight, I should have looked for "unit_chunk" in the structure docs.